Correction fluids are used for correcting handwritten, typewritten, photocopied, or laser printed markings on paper. Generally, correction fluids are applied to a paper surface over an erroneous marking in liquid form. The fluid subsequently forms a film which effectively covers erroneous markings on the surface and can receive a correct marking. Making a corrective marking over the film commonly is known as "writeover".
Correction fluids typically include some standard ingredients, including an opacifying pigment (commonly titanium dioxide), a film-forming polymeric material, and a solvent. The opacifying pigment is dispersed in the fluid and provides the basic white color which can be toned with other pigments to provide a correction fluid closely corresponding to the color of the paper to which the fluid is to be applied. The opacifying pigment functions to obscure the erroneous marking over which the correction fluid is applied. The film-forming polymeric material, also known as the binder, binds the pigment to the paper and helps to form a flexible but continuous covering that remains once the solvent has dried.
The solvent is used as the carrier for the other ingredients in the fluid. The solvent can be either a volatile organic or water. Volatile organic solvents have the advantage of evaporating quickly and as a result correction fluids based on volatile organic solvents often are ready to receive a corrective marking 15-20 seconds after application. In contrast, commercial water-based correction fluids typically are not ready to receive a corrective marking until about 90 seconds after application. But water-based correction fluids generally are better for the environment and safer than correction fluids including volatile organic solvents.